1. Field of the Invention
The present invention relates to a transmission for a work vehicle having PTO function for transmitting a force to an implement mounted on a vehicle body.
2. Description of the Related Art
With the transmission of the above-noted type, conventionally, as known from e.g. Japanese Patent Application “Kokai” No.: Sho. 58-102848 (FIGS. 1 and 3), a drive force from an engine is divided between a vehicle traveling force and an implement driving force through first and second multiple-plate friction clutches and an intermediate transmission shaft included in the first multiple-plate friction clutch, respectively. The implement driving force from the intermediate transmission shaft is inputted to a PTO change-speed mechanism housed in a transmission case, so that the force is subjected to a change-speed operation by this PTO change-speed mechanism and then this speed-reduced force is transmitted to a rear PTO shaft. On the other hand, the vehicle traveling force from the first and second multiple-plate friction clutches is subjected to an auxiliary change-speed operation by an auxiliary change-speed mechanism including small and large gears mounted on a change-speed shaft and a shift gear mounted on a bevel-pinion shaft and then this force is transmitted to a rear-wheel differential mechanism.
In the case of this conventional work vehicle transmission having PTO function, in the number of speeds available from the auxiliary change-speed mechanism is to be increased, this will result in enlargement of the auxiliary change-speed mechanism, thus requiring a large space for accommodating the mechanism. This then requires enlargement of the differential case. Such enlargement of the differential case results in increase of the wheel base of the vehicle. For avoiding such increase of wheel base, there arises the necessity of reducing the length of the transmission case which is formed separately from the differential case and which accommodates such mechanisms as a main change-speed unit for traveling, a reduction mechanism for the implement. However, if the length of the transmission case is reduced, this will impose significant restriction in the spatial arrangement of the above-described components accommodated within the case.
In the case of a further conventional transmission known from Japanese Utility Model Application “Kokai” No. Hei. 1-11550 (FIGS. 3 and 5), a rear PTO shaft (shown at 1 in FIGS. 3 and 5 of the document) is disposed at a rear portion of the vehicle body and a mid PTO shaft (shown at 3 in FIGS. 3 and 5) is disposed forwardly of the rear PTO shaft. With this arrangement, for instance, if a lawn mower implement is disposed between the front wheels and the rear wheels and a grass collector and a blower are disposed on the rear portion of the vehicle body, the lawn mower implement can be driven by the mid PTO shaft and the blower can be driven by the rear PTO shaft so that grass or lawn cut by the mower can be drawn by the blower to be collected into the collector. With the work vehicle having this type of transmission, there often occurs a situation of the lawn mower implement being driven by the force from the mid PTO shaft. For this reason, it is necessary to transmit high-speed force to the mid PTO shaft and to dispose this mid PTO shaft at a low position. Further, the force from the engine is transmitted to a transmission gear (shown at 38 in FIGS. 3 and 5) and force from this transmission gear is transmitted from a switchover slider (shown at 36 in FIGS. 3 and 5) through a retaining portion and a transmission shaft (shown respectively at 37 and 11 in FIGS. 3 and 5) to the rear PTO shaft. The force from the transmission gear (shown at 38 in FIGS. 3 and 5) is transmitted via the switchover slider (shown at 36 in FIGS. 3 and 5) through transmission gears (shown at 35, 42 in FIGS. 3 and 5) to the mid PTO shaft disposed at the low position. In this case, the transmission gears are set to provide an accelerating gear ratio for transmitting a high-speed force to the mid PTO shaft. With the transmission of the above construction, a transmission gear is mounted coaxially relative to a transmission gear receiving the power from the engine, which transmission gear is meshed with a transmission gear mounted on the mid PTO shaft. In this case, there is a limit in possible enlargement of the transmission gear for transmitting high-speed force to the mid PTO shaft (this is probably attributable to the fact the transmission gear acts as a point of force division between the force to the rear PTO shaft and the force to the mid PTO shaft). Hence, it is necessary to allow transmission of high-speed force to the mid PTO shaft by minimizing the diameter of the transmission gear mounted on the mid PTO shaft. However, if this transmission gear (shown at 3 in FIGS. 3 and 5) mounted on the mid PTO shaft is reduced in diameter, this will result in corresponding rising of the disposing position of the mid PTO shaft.